The present invention relates to an ink droplet detecting apparatus for use in an ink jet printer and in particular, to an apparatus for detecting the flight path and/or speed of an ink droplet.
Ink jet printers, especially ink-on-demand type ink jet printers provide quiet printing, however, they suffer from the disadvantage that the flight of ink dropolets becomes unstable or impossible when the printer is subjected to rough handling. It has been proposed to solve this problem in a variety of ways so that upon the malfunction of an ink jet head, printing is stopped, the printing apparatus recovers, or a similar step is performed based upon the detection of ink droplet condition. One such proposal provides a method for a detecting unsatisfactory flights of ink droplets by determining the presence of air bubbles in a pressure chamber by detecting the drive waveform of a piezoelectric element. Another proposal is a method for detecting an ink droplet speed, by detecting the current induced by a charged ink droplet which has been ejected by a nozzle.
These proposed methods suffer from disadvantages in that they provide a low detection sensitivity, need a high voltage to function or require a costly and complicated circuit. Accordingly, it is desirable to provide an ink droplet detecting apparatus which overcomes the shortcomings of the previously proposed methods of detection described above.